[Zope] - Zope, DTML and XML

[Jim Fulton]

Paul Prescod wrote:
> 
> Of course Zope must eventually move into the XML world. Zope needs to do
> templates.

It already does, via DTML.

> XSL also does templates.

I would have thought that XSL *was* a template mechanism.  What do you mean
by "template"?

> In fact templates are almost as central to XSL as they are to Zope.

I would say far more so,

> I would suggest that Zope should use
> XSL template syntax for DTML templates as far as is possible.

It appears to me that DTML and XSL represent two very different
approaches to solving the same or similar problems.  They are
both intended for generating text from objects.  DTML generates text
from Python objects.  XSL generates text from XML objects.

DTML takes a higly procedural approach.  In DTML, you generate
text directly.  In XSL (as I understand it) you specify a set of
rules for applying transformations to XML elements.  This is fairly 
declarative in nature.  In the example you gave, you didn't render a 
specific picture element.  Instead, you have a rule for converting
picture elements to img tags.

Another difference between DTML and XSL is in how content is determined.
DTML is typically used to define as well as format content.  A DTML 
document directly specifies data that is often extracted from large
object spaces.  In XSL, it appears that the content is largely defined
by a source document and an XSL "template" simply specifies transformations.
Of course, an XSL specification can also filter, so there is some
ability to extract, but it is much less direct than with DTML.

Given the very different natures of DTML and XSL, I don't see much
point in making the syntaxes all that consistent. 

> In fact,
> maybe when XSL becomes popular enough, it might make sense to describe the
> interaction between Zope and the Python runtime in terms of XML
> transformations.

It may very well. If Zope made it easy to generate XML from Zope (ie Python)
objects, then people who  like XSL could apply XSL transformations to the
resulting XSL, bypassing DTML altogether.

In other words, I see XSL as an alternative to DTML, not another form of it.

Or, DTML may turn out to be a good tool for generating XML from objects, and
then XSL could be applied to DTML output, in which case the two would
act in tandem.

Jim

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